Adverse experiences during licensed treatment with the antidepressant serotonin (5-HT) reuptake inhibitor zimeldine in Sweden are presented. Data were obtained from a written inquiry of 694 patients and 67 reports to the Medical Products Agency. The spectrum of adverse symptoms was in agreement with those reported in previous studies on zimeldine. The most frequent adverse experiences were headache, nausea, myalgia, signs of liver function disturbance, arthralgia, neurological symptoms, fever and insomnia. No new case of the Guillain-Barré syndrome was found. The estimated frequency of the zimeldine-induced hypersensitivity syndrome (HSS), comprising fever, myalgia and/or arthralgia and signs of liver function disturbance, ranged from 1.4% to 13% in the inquiry and from 0.63% to 3.4% in the report part of the study. Adverse experiences usually had a considerably higher incidence during the first 6 weeks of zimeldine treatment than thereafter. This is in agreement with the clinical experience that most of the adverse reactions occur early during zimeldine treatment. However, a number of adverse experiences did occur with a later onset. This may justify a prolongation of the compulsory 4 weeks' testing of liver function that is required during licensed treatment. There were significantly fewer patients who developed fever among the patients who had experienced previous zimeldine treatment than among those who had not. Otherwise there was no statistically significant difference in frequency of adverse symptoms between these two groups. Consequently zimeldine treatment per se does not seem to predispose to development of an HSS or other types of adverse reactions during subsequent therapy.